From Big Medical Encyclopedia

ISOENZYMES (synonym: multiple forms of enzymes, isozymes) — molecular forms (versions) of a certain enzyme differing only on physical and chemical properties; definition an isoenzyme-nogo of a range of various enzymes in blood serum is one of important methods a wedge, enzimodiagnostik. And. are found in tissues of the person, animals, plants and microorganisms. It is known the St. 50 enzymes presented in the form And. in various bodies and tissues of the person, animals and plants.

And. can differ from each other on quarternary structure, i.e. on character and the number of the subunits which are a part of their molecules on electrophoretic mobility, the adsorptive properties, affinity to substrate, an optimum pH value, subcellular localization, specificity in the relation coenzymes (see) etc. So, e.g., most bodies and tissues of the person and animals supports five And. lactate dehydrogenases (LDG), each of which represents various combinations from four subunits of two types about a pier. the weighing 34 500, conditionally designated «N» and «M» (see. Lactate dehydrogenase ). Both types of subunits differ on amino-acid composition, the sequence of the remains of amino acids in a molecule, to immunochemical and electrophoretic properties. Synthesis of subunits is controlled by two various genes. The malate dehydrogenase (MDG) is presented in various tissues of the person and animals by two And., one of which is localized in mitochondrions, and another — in cytoplasm. Both these And. differ on specificity in the relation OVER and sensitivity to inhibitors (e.g., to oxalate). And. isocitratedehydrogenases (ITsDG; KF 1.1.1. 41 and differ on specificity to coenzymes (NAD and NADF), and also on subcellular localization: NAD-ITSDG is localized in mitochondrions, and NADF-ITsDG both in mitochondrions, and in cytoplasm. Mitochondrial and cytoplasmatic NADF-ITsDG differ among themselves on catalytic, electrophoretic and immunochemical properties.

For identification and division And. use various physical. - chemical methods of a research: different types electrophoresis (see), the adsorptive and ion-exchange chromatography (see), gel filtering (see), etc. The most wide spread occurance as the most available received a method of an electrophoresis in polyacrylamide gel (disk electrophoresis). Distinctions in electrophoretic properties are a basis for classification of many And. For designation I. the reduced name of enzyme with the corresponding interlinear sequence number which characterizes electrophoretic mobility is provided And. at a certain pH value. E.g., And. lactate dehydrogenases are designated as LDG1, LDG2, LDG3 etc.

Biol, value of existence of multiple forms of enzymes is not clear yet. Assume, as. play a part in regulation of metabolic processes in a cell. Perhaps, as. provide adaptability of an organism to changes of the environment and cause the specificity of exchange characteristic of this fabric. Therefore many enzymes taking key positions in a metabolism have And. (LDG, MDG, enzymes catalyzing oxidizing phosphorylation, various aminotransferases). It is possible that various And. the same enzyme specifically catalyze direct or return reactions of a certain enzymatic reaction (see. Lactate dehydrogenase ). About an important role And. in thin regulation of metabolic processes change of their range under the influence of a number of influences and fiziol, factors testifies (denervations, various hormones, cooling, a hypoxia, etc.). Change in the nature of distribution various is noted And. in tissues of the person and animals in an embryogenesis. However for the studied enzymes specific embryonal forms I are not found yet.

Range And. in the quantitative and qualitative relation in various tissues of the person and animals it is various and often strictly specific. It has great diagnostic value. As biosynthesis separate And. and their subunits it is controlled by various genes, assume that modification of a gene involves emergence atypical And. in fabrics and blood. Thus, there is a possibility of use of definition of ranges And. for diagnosis of genetic anomalies. Row patol. processes, especially degenerative and destructive character, it is connected with change of permeability of cellular membranes that is the reason of change of a range And. in blood serum of the patient. Therefore definition And. in blood and tissues of the person finds more and more broad application in clinic. For the solution of some questions of diagnosis, a pathogeny and therapy of a number of diseases definition of isofermental ranges has essential advantage in comparison with definition of the general activity of this or that enzyme. The greatest diagnostic value has definition an isoenzyme-nogo of a range of LDG which changes at a myocardial infarction (activity of LDG1 and LDG2 sharply increases). Changes of a range And. LDG in blood serum remain longer, than changes of total activity of enzyme, and can be found when the general activity of LDG is returned to norm. Deviations of a range And. LDG from norm are noted at diseases of gepatobiliarny system, at muscular dystrophies, tumoral diseases, an acute leukosis, patol, processes in lungs (acute focal and croupous pneumonia, an aggravation hron, pneumonia, etc.)*.

As diagnostic test serve also changes of ranges And. and other enzymes, napr, significant increase in the MDG cathode fractions (in particular mitochondrial fraction) in blood serum of patients with cirrhosis but to comparison with blood serum of patients hron, hepatitis. Definition of a range And. and finds for the general activity of MDG in blood broad application for diagnosis and assessment of weight of asphyxia for newborns. Changes of activity And. acid phosphatase are noted at a disease to Gosha (see. to Gosha disease ), prostate cancer and multiple myeloma. For diagnosis of a number of diseases of a liver use definition of a range And. an alkaline phosphatase (see. Phosphatases ).

Definition And. aminotransferases (see) also has diagnostic value. In a liver, kidneys, a cardiac muscle of the person two are found And. aspartate aminotransferases (KF; ASAT). One of them is localized in mitochondrions, another — in cytoplasm of cells. Apprx. 79% of all activity of ASAT falls to the share mitochondrial And. and only 21% for a share of cytoplasmatic. At heavy disease of Botkin in blood serum it is found two And. ASAT whereas is normal also at the easy course of a disease — only one.

At injuries of skeletal muscles, and also at a myocardial infarction in blood serum activity increases creatine kinases (see), and also its range changes And.

Bibliography: Genetics of isoenzymes, under the editorship of D. K. Belyaev, M., 1977, bibliogr.; Ivanov I. I., Cows of N of B. F. and M and r to e of l about in I. M. Introduction in clinical enzymologies), L., 1974, bibliogr.; Mosquitoes F. I., Korovkin B. F. and Menshikov V. V. Biochemical researches in clinic, L., 1976; Lenindzhsr A. Biochemistry, the lane with English, page 217, etc., M., 1976; Problems of medical chemistry, under the editorship of V. S. Shapot and E. G. Larsky, page 5, M., 1973; Wu Yi of l to and N with about N of. Isoenzymes, the lane with English, M., 1968; Achievements of biological chemistry, under the editorship of V. L. Kretovich, etc., t. 9, page 55, M., 1972; Enzyme nomenclature, Amsterdam, 1965; To and r 1 a n N. Lake of Symposium on multiple forms of enzymes and control mechanisms, Bact. Rev., 'v. 27, p. 155, 1963; Latner A. L. Isoenzymes, Advanc. clin. Chem., v. 9, p. 69, 1967.

L. V. Pavlikhina.